The present invention relates to a device for detecting the level of a liquid contained in a tank, in particular for detecting the level of the fuel contained in the tank of a motor car and generating a corresponding electric signal.
The device comprises a substantially cylindrical container adapted to be inserted in the tank, a vertical bar disposed longitudinally inside the cylindrical container and a float movable with respect to the bar to follow the variations in the level of the liquid.
A device of this type is known from U.K. Patent Application No. 2,130,733. in which a wire acting as a variable resistor is wound on the bar and in which a sliding contact held resiliently against the wire of the bar is mounted on the float. A pair of spiral springs of metal and very flexible are disposed one above and the other below the float, coaxially with the bar, in such manner as not to touch the wire which is wound around the bar itself. The upper spring permanently connects the sliding contact mounted on the float to a terminal outside the container. The electrical resistance between this external terminal and the upper end of the wire wound on the bar is inversely proportional to the level of the fuel and is utilized to generate the desired electric signal.
The presence of the metal springs coaxial with the bar and close to the wire which acts as a variable resistor makes this device not very reliable, however, above all if used in unstable conditions of the tank; in fact, rocking and/or tilting of the latter may cause undesired contacts between the metal springs and the wire wound on the bar and, consequently, generate an electric signal not corresponding to the actual level of the liquid in the tank.